1. Field of Inventions
The present invention relates generally to a signaling method for a pen driver circuit interface and, more specifically, to a signaling method employing a pen driver circuit to process a combination of signals including at least one signal from a signal interface in order to provide information associated with a signal line which has been eliminated from the signal interface.
2. Description of the Related Art
FIG. 1 shows a controller/driver/pen system 100 including a controller circuit 102, a pen driver circuit 104 and a pen 106 for a printer. The system 100 includes a conventional serial interface 108 between the controller circuit 102 and the pen driver circuit 104. The system 100 also includes a conventional signal interface 110 between the pen driver circuit 104 and the pen 106.
Generally, the digital pen controller 102 is responsible for communicating with the analog pen driver integrated circuit ("IC") 104 to control the InkJet pens. More specifically, the controller circuit 102 provides data and timing information to the pen driver circuit 104 to fire drops of ink. Also, the controller circuit 102 monitors the pen head temperature and pulse-warms the pen 106 if it is not warm enough to maintain acceptable print quality.
FIG. 2 shows a timing diagram 200 of the signals typically found in such systems, namely, CLOCK 202, DATA 204, LOAD 206, FIRESTROBE 208, and WARMSTROBE 210 (the names of the signals may vary, but the functions are usually the same). In this example of a typical signaling scheme, the CLOCK signal 202 is used to shift data bit-by-bit over the DATA signal 204 from the digital application-specific integrated circuit ("ASIC") 102 to the pen driver IC 104. A single bi-directional DATA signal 204 is shown because some status information could be returned from the pen driver IC 104 on the same line when data is not being transferred in. Some systems may have multiple DATA signals. Once all of the data bits have been shifted into an internal shift register of the pen driver IC 104, the rising edge, for example, of the LOAD signal 206 transfers the shift register contents into an internal control register of the pen driver IC 104. This loading step is necessary to prevent the pen driver IC 104 from responding to the shifting data as the bits trickle over each of the various control bit positions. Once the data has been transferred and loaded, firing and warming may begin.
For the sake of simplicity, the timing diagram 200 shows both the FIRESTROBE signal 208 and the WARMSTROBE signal 210 being asserted on the same transfer. This may or may not be the case. The FIRESTROBE signal 208 causes pen nozzle resistors in the pen 106 which have been selected by the transferred data to be driven with electrical current for a sufficiently long period of time to heat the resistor to a high enough temperature to fire a drop of ink. The WARMSTROBE signal 210 is used to drive current through all of the nozzle resistors, regardless of which nozzles have been selected for firing. The WARMSTROBE pulse 210 is generated for a sufficiently long period of time to heat the nozzle resistors (and therefore the pen head), but is short enough in duration to avoid firing ink out of the nozzles.
FIG. 9 is a schematic of an exemplary conventional multiplexing circuit 900 for controlling nozzles in a printhead of a printer which has sixteen (16) groups of nozzles, with four (4) nozzles in each group. The multiplexing circuit 900 includes nozzle group selection logic 902, AND-gates 904, 906, 908 and 910, OR-gates 912, 914, 916 and 918, and AND-gates 920, 922, 924 and 926 configured as shown.
In operation, only one nozzle group is selected at a time via the four group select bits provided as inputs to the group selection logic 902. By way of example, when group `n` is selected, all four nozzles in group `n` are driven whenever the "Warm Enable Pulse" 210 is asserted. If the "Warm Enable Pulse" 210 is not asserted, any of the nozzles in group `n` will be driven whenever the "Fire Enable Pulse" 208 is asserted and the corresponding "Select Bits" for those nozzles are asserted. If neither the "Warm Enable Pulse" 210 or the "Fire Enable Pulse" 208 is asserted, no nozzles are driven. In logic terms, a nozzle is driven when: (its group is selected) AND ((the "Warm Enable Pulse" 210 is asserted) OR (the "Fire Enable Pulse" 208 is asserted AND the nozzle is selected)).
A drawback of the above-described signaling implementation is that five signals are required to perform all of the functions necessary to provide data shifting, data loading, and independent nozzle firing and pulse warming.
A possible solution would be to make the pen driver IC 104 more "intelligent" so that it can automatically warm and fire the pen 106 once data has been received from the digital controller 102. Such a system could theoretically have a pen driver IC 104 with only one control signal that uses a self-clocking serial data transfer protocol to receive data from the digital controller ASIC 102. Once all the data has arrived, the "smart" pen driver IC 104 would wait an appropriate amount of time per its programming before firing the pen 106, and would also monitor the pen head temperature to automatically warm the pen 106 without intervention from the digital ASIC 102. While such an approach would provides a single control signal, it requires a more complex pen driver IC 104. Pen driver ICs are power devices designed to drive high currents at high voltages; however, they are not well suited for containing control logic. Furthermore, such a "smart" pen driver 104 would require a phased-locked loop ("PLL") to synchronize with the data stream on the single control line since there is no dedicated clock.
Another possible solution would be to provide a twowire signal interface having just CLOCK and DATA signals. Although such a signal interface would not require a PLL, the pen driver circuit 104 would still need to automatically control the timing of the firing and warming events, which would require on-chip timers and an oscillating clock circuit on the IC 104 or on the printed circuit board ("PCB").
In summary, the addition of a PLL and/or timers to the pen driver circuit 104 increases the complexity and cost of the pen driver IC 104 by adding circuitry that analog fabrication processes are not well suited for. Additionally, placing control of the firing and warming timing in the pen driver IC 104 could reduce flexibility, possibly making the IC 104 less desirable to be used in future products. If the pen driver IC 104 is located on a carriage printed circuit assembly ("PCA"), an oscillating clock at the carriage would also have increased radiated emissions at radio frequencies, which may require extra cost to suppress in order to satisfy regulatory requirements.
Thus, a need exists for a control interface to an InkJet pen driver IC that provides lower system cost without sacrificing functionality, namely, a pen driver IC signaling implementation which provides the full functionality and information content of a conventional control interface and reduces the number of control signals, without adding a significant amount of circuitry to the pen driver circuit.